In the printing industry, fluid metering or transfer rolls are used to transfer measured amounts of ink onto printing plates. The rolls are generally referred to as anilox rolls. In other industries, liquid glue or other substances can be transferred onto surfaces of various substrates. The metering rolls are generally engraved with an array of closely spaced, shallow depressions referred to as cells. In the printing industry, ink is fed into the cells and onto the transfer surface of an anilox roll from an ink transfer roll turning within an ink bath. To remove the excess ink from the anilox roll surface, a doctor blade is scraped against the roll so that excess ink is removed and the remaining ink on the anilox roll is contained only in the cells. The ink in the cells is then transferred to a substrate, such as a polymer or paper material. The design or image formed by the ink cells is thus imprinted on the substrate.
The anilox roll is generally cylindrical and may be constructed in various diameters and lengths, containing cells of various sizes and shapes. The volumetric capacity of an anilox roll for a fluid such as ink is dependent upon the selection of cell size and shape, and number of cells per unit area. The cell pattern or design may be fine (many small cells per square inch ) or coarse (fewer larger cells per square inch). Anilox rolls having high cell density are used for high-quality printing and rolls having the largest cells are used in non-printing applications such as the application of glue or paint.
Within the printing industry, the volumetric capacity of an anilox metering roll is specified as a combination of metric and English units (billions of cubic microns per square inch [BCM/inch.sup.2 ]) and can vary from one billion cubic microns per square inch to possibly 500 billion cubic microns per square inch (one BCM=1 microliter). In a conventional printing operation, the anilox roll is forced against a printing plate and against a doctor blade during ink transfer with the result that surface friction wear occurs. This surface wear of the anilox roll can reduce the volume of the anilox roll. To maintain high quality printing applications or non-printing applications such as applications of glue or paint, it is necessary to accurately determine the volumetric capacity of the roll from time-to-time. Since the cell structure of most anilox rolls is too small to be observed by the naked eye, a metallurgical microscope is usually required for cell inspection and evaluation.
Previous attempts to determine the volumetric capacity of the anilox roll was to make measurements with a metallurgical microscope however, this procedure has not been satisfactory or accurate enough. The microscope may be used for direct examinations of the transfer cell structure, or indirectly by examinations of a molded replica of the cell structure. In either case, the determination of cell volume requires mathematical calculations which can often be inexact. The particular mathematical formula to be used will depend on the overall shape of the cells and the material used for the roll.
U.S. Pat. No. 4,628,728 discloses a method for measuring the volumetric capacity of an anilox roll by depositing a measured amount of ink onto the surface of an anilox roll and the area that the measured amount of ink will cover is determined. The ink is dispensed from a precision micro pipette directly onto the surface of the anilox roll. A sheet of transfer material having low absorbency is then spread over the roll and the ink deposit lying between the anilox roll and the transfer sheet is spread by the application of a scraper blade across the backside of the transfer paper. The engraved cells are filled by the excess ink as it is spread across the cell transfer surface. Upon completion of spreading of ink deposit, the transfer paper is carefully removed and allowed to dry. The area of the transfer paper impression is then measured by overlaying the impression area with a transparent sheet of graph paper having suitable grid lines. The known quantity of ink deposited upon the roll (in billions of cubic microns or microliter) is then divided by the measured area of the transfer impression (in square inches), with the quotient being the volumetric capacity of the roll in billions of cubic microns per square inch.
It is an object of the present invention to provide a method for measuring the volumetric capacity of a selected surface having engraved cell using fluorescent means.
It is another object of the present invention to provide a method for measuring the volumetric capacity of an anilox roll using fluorescent means.
It is another object of the present invention to provide a simple, direct and efficient method for measuring the volumetric capacity of a cell-engraved roll, such as an anilox roll.